OK i think you are right in most of your assumpitions- except on the part of productivity of low skilled people. Anyperson who can support his own weight in any economy should be logically a benefit in that economy is what I am arguing- be it a high productive one or a low productive one(obviously the high productive one is more valuable but that does not mean low productive one , so long as he does not smooch off others is a bad thing on the economy)!
Coming to my argument, for example, hypothetically, let us say tomorrow, a huge invention takes place and we have robots like that in the I Robot movie, which does all the low level manual Human work like carpenting, works in agriculture, coal fields for 50% of the cost of employing human labor, would you accept such robots into our country or not. Will it be beneficial to our country or not? Explain why?
Productivity of low-skilled people:
The goal is to improve the productivity of the economy and make sure people move up the value chain. A coolie wants his son to be a driver, a driver wants his son to be a bank clerk, a bank clerk wants his son to be an officer, an officer wants his son to be a well-paid high-flying engineer, etc. etc.
If everyone in the above list produces 10 kids, resulting in a total of 40 kids, you need to add enough jobs for 40 drivers, clerks, officers and engineers. If you add less engineer jobs, officer's sons would have to remain officers. If you add less officer jobs, clerk sons would have to remain clerks. If you add less driver jobs, coolie sons would have to remain coolies.
600 million Indians are currently coolies, to put it simply and crudely. You can say that they are "supporting their own weight" in the economy. But in reality, this is classic "disguised unemployment". Lets say, 100 coolies are necessary to tend to 5 fields of 1 acre each. If these 5 fields are consolidated, mechanization is introduced, yield increases greatly. And you need only 10 coolies. Remaining 90 coolies will "move up the value chain" due to getting absorbed in industry, services, etc.
If you don't pull the coolies out and up the value chain, you can say that they are "supporting their own weight", but the goal of improving the productivity of the economy and making people move up the value chain is not happening.